Preliminary evidence suggests that the polypeptide composition of dengue virions derived from mosquito cell cultures show host cell modification when compared to virus replicated in mammalian cells. In addition, the host cell response of the two systems grossly show differences. The cellular basis of these differences will be explored. A suitable system of 1) a continuous mosquito cell line free of contaminating viruses; 2) appropriate group B togaviruses and bunya viruses capable of replicating to high titer in the mosquito cells, and 3) proper conditions for labelling progeny virus, will be sought. Virus growth curves will be constructed and the polypeptide composition of viruses replicated in mosquito and in mammalian cells will be determined. Preliminary work suggests that a fourth polypeptide is present in dengue virus produced in mosquito cells and that this additional protein is derived from the host cell membrane. This will be further examined by SDS polyacrylamide slab gel electrophoresis, and the origin of the proteins (viral vs. host cell) will be studied by immunologic methods. Virus production under various conditions such as low or high temperature and deficient or complete nutrient media will also be examined.